It is conventional practice in systems for recovering refrigerant from equipment under service to employ a refrigerant compressor both for pumping the refrigerant from the equipment and drawing a vacuum at the equipment preparatory to recharging the equipment with fresh refrigerant. Such a system is shown, for example, in FIG. 5 of U.S. Pat. No. 4,805,416 assigned to the assignee hereof. Typically, refrigerant compressors are designed for air conditioning and refrigeration applications with specified design criteria for the compression ratio and pressure differential across the compressor. However, U.S. EPA regulations and guidelines regarding the final recovery vacuum obtainable by refrigerant recovery systems to prevent refrigerant mixing exceeds the design parameters of typical refrigerant compressors. Various techniques have been proposed for reducing the recovery system compression ratio or cooling the compressor, or for providing compressors of special design. However, such proposals are expensive and provide less than satisfactory results. It is therefore a general object of the present invention to provide a refrigerant handling system and method, and more specifically a refrigerant recovery system and method, that obtains improved recovery vacuum in the equipment under service while employing conventional components of proven capability and standard cost.
A refrigerant handling system in accordance with presently preferred embodiments of the invention includes a compressor having an inlet for connection to a source of refrigerant to be pumped. Such source may comprise refrigeration equipment from which refrigerant is to be recovered, or a refrigerant storage container from which refrigerant is to be pumped either to another container or to recharge evacuated refrigeration equipment. A vacuum pump is selectively connectable in series with the compressor during a latter portion of the pumping cycle to assist the compressor in removing all refrigerant from the refrigerant source while at the same time drawing a deeper vacuum at the source than would otherwise be obtainable using the compressor alone. In the preferred embodiments, a sensor or gauge is connected at the refrigerant inlet for indicating refrigerant pressure, and a valve is either automatically or manually responsive to inlet refrigerant pressure for connecting the vacuum pump to the refrigerant compressor when inlet refrigerant pressure falls below a selected level. Thus, for example, the refrigerant compressor may be employed alone for drawing refrigerant down to a pressure of one atmosphere (zero psig, 29.9 inches of mercury), and the vacuum pump then operatively connected in series with the compressor to assist the compressor in drawing a deeper inlet vacuum in the range of zero to twenty inches of mercury.
A refrigerant recovery system in accordance with the preferred embodiments of the invention includes a compressor having an inlet and an outlet, and an oil separator connected to the compressor inlet for separating oil from refrigerant recovered from equipment under service. A check valve is connected between a vapor outlet port on the oil separator and the inlet of the compressor for feeding refrigerant directly to the compressor inlet. A pressure sensor or gauge is connected to the oil separator for indicating refrigerant vapor pressure within the separator, and a valve is automatically or manually responsive to such refrigerant vapor pressure for connecting a vacuum pump between the oil separator vapor port and the compressor inlet in parallel with the check valve when refrigerant vapor pressure at the oil separator falls below a predetermined value.